Capacitive mouse

ABSTRACT

A pointing device some or all of whose elements are made from capacitive sensors. Such elements may include a rotary motion detector which includes a rotating member and a plurality of fixed capacitive detecting members; a rolling ball with patterned conductive surface and a plurality of fixed capacitive detecting members; capacitive touch sensors or capacitive switches to serve as mouse buttons; and a scrolling wheel, knob, or touch surface built from capacitive sensors. The pointing device further includes a capacitance measuring circuit and processor to measure variations of capacitance on the various capacitive elements and to determine the movement of and other activations of the mouse.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/253,477 filed on Oct. 18, 2005 which is a continuation of U.S. patentapplication Ser. No. 10/382,799, filed Mar. 5, 2003 which is now U.S.Pat. No. 7,212,189, which is a continuation of U.S. patent applicationSer. No. 09/971,181, filed Oct. 4, 2001, which is a divisional of U.S.Pat. No. 6,587,093, filed Nov. 3, 2000, which claims priority to U.S.Provisional Application Ser. No. 60/163,635, filed Nov. 4, 1999.

BACKGROUND OF THE INVENTION

This patent discloses a computer mouse implemented partially or whollyusing capacitive sensors. Pointing devices are an essential component ofmodern computers. One common type of pointing device is the mouse.Computer mice have been well known for many years. U.S. Pat. No.3,541,541 to Engelbart discloses an early mouse implementation usingeither potentiometers or wheels with conductive patterns to measure themotion. The conductive patterns on these wheels are measured by directelectrical contact. Direct electrical contact to moving objects has manywell-known disadvantages, such as increased friction, and wear andcorrosion of contacts.

Modern mice follow a plan similar to that of U.S. Pat. No. 4,464,652 toLapson et al, with a rolling ball mechanically coupled to optical rotarymotion encoders. The mouse also includes one or several buttons thatoperate mechanical switches inside the mouse. Recent mouse designs alsofeature a wheel for scrolling; U.S. Pat. No. 5,530,455 to Gillick et aldiscloses a mouse with a scroll wheel mechanically coupled to anotheroptical rotary encoder. Such mechano-optical mice are widely used andwell understood, but they do suffer several drawbacks. First, as movingparts they are susceptible to mechanical failure and may need periodiccleaning. Second, they are exposed to dirt, moisture, and othercontaminants and environmental effects. Third, as low-cost mechanicaldevices they may be less sensitive to fine movements than fullyelectronic devices. Fourth, electromechanical sensors may be moreexpensive than purely electronic sensors. And fifth, optical sensorsdraw a significant amount of power due to their use of light emittingdiodes.

Another well-known type of mouse measures motion by direct opticalsensing of the surface beneath the mouse. U.S. Pat. No. 4,364,035 toKirsch discloses an optical mouse that worked with patterned surfaces,and U.S. Pat. No. 5,907,152 to Dandiker et al discloses a moresophisticated example that works with natural surfaces. U.S. Pat. No.5,288,993 to Bidiville et al discloses a pointing device which includesa rotation ball but measures the rotation of the ball by purely opticalmeans. Optical mice eliminate the difficulties associated with movingparts in the motion sensor, but even they must typically use mechanicalmouse buttons and a mechanical scroll wheel.

Many alternatives to scroll wheels have been tried. U.S. Pat. No.5,883,619 to Ho et al discloses a mouse with a four-way scrollingbutton. U.S. Pat. No. 5,313,229 to Gilligan et al discloses a mouse witha thumb-activated scrolling knob. U.S. Pat. No. 5,122,785 to Cooperdiscloses a mouse that is squeezed to initiate scrolling. TheScrollPoint Mouse from International Business Machines includes anisometric joystick for scrolling, and the ScrollPad Mouse from Fujitsuincludes a resistive touch sensor for scrolling. The proliferation ofsuch devices shows both that there is a need for a good scrolling devicefor use with mice, and that none of the technologies tried so far arecompletely satisfactory.

Capacitive touch pads are also well known in the art; U.S. Pat. No.5,880,411 discloses a touch pad sensor and associated features. Touchpads can simulate the motion detector and buttons of a mouse bymeasuring finger motion and detecting finger tapping gestures. Touchpads can also be used for scrolling, as disclosed in U.S. Pat. No.5,943,052. Capacitive touch pads are solid state electronic devices thatavoid many of the pitfalls of mechanical sensors. However, many usersprefer mice over touch pads for reasons of ergonomics or familiarity.

Capacitive touch sensors for use as switches are well known in the art.For example, U.S. Pat. No. 4,367,385 to Frame discloses a membranepressure switch that uses capacitance to detect activation. U.S. Pat.No. 5,867,111 to Caldwell et al discloses a capacitive switch thatdirectly detects the capacitance of the user. The circuits of the '411patent already cited could also be used to implement a capacitiveswitch. Applications of capacitive switches to mice are relatively rare,but in the paper “Touch-Sensing Input Devices” (ACM CHI '99, pp.223-230), Hinckley and Sinclair disclose an experimental mouse withcapacitive touch sensors to detect the presence of the user's hand on ornear various mouse controls.

U.S. Pat. No. 5,805,144 to Scholder et al discloses a mouse with a touchpad sensor embedded in it. However, Scholder only considers resistiveand thermal touch sensors, which are less sensitive and less able to bemounted within the plastic enclosure of the mouse than capacitivesensors. Scholder suggests using the touch sensor in lieu of mousebuttons, but does not consider the use of the touch sensor forscrolling.

The purpose of the present invention is to create a device with thefamiliar form and function of a mouse, wherein some or all of themechanical functions of the mouse have been replaced by capacitivesensors.

SUMMARY

The present invention is directed toward a pointing device similar to aconventional mouse, but some or all of whose elements are made fromcapacitive sensors. Such elements may include a rotary motion detectorwhich includes a rotating member and a plurality of fixed capacitivedetecting members; a rolling ball with patterned conductive surface anda plurality of fixed capacitive detecting members; capacitive touchsensors or capacitive switches to serve as mouse buttons; and ascrolling wheel, knob, or touch surface built from capacitive sensors.The pointing device further includes a capacitance measuring circuit andprocessor to measure variations of capacitance on the various capacitiveelements and to determine the movement of and other activations of themouse.

The disclosed device is directed towards a computer mouse. The computermouse comprises a touch sensor embedded within a surface material of themouse. The touch sensor is configured to measure motion of a fingeralong an axis. The touch sensor is configured to operate by capacitivemeans.

Another embodiment disclosed includes a pointing device. The pointingdevice comprises a computer mouse configured to generate cursorcommands. A touch sensor is coupled to the computer mouse. The touchsensor is configured for measuring motion of a finger along an axis. Thetouch sensor is configured for operating by capacitive means. Aprocessor is in operative communication with the touch sensor. Theprocessor is configured to generate a scrolling command in response tothe motion of the finger along the axis. The processor is configured tocontinue generating the scrolling command responsive to the fingerlifting from the touch sensor.

Another embodiment disclosed includes a touch input system. The touchinput system comprises a capacitive touch sensor configured formeasuring motion of a finger along an axis. A processor is in operativecommunication with the capacitive touch sensor. The processor isconfigured to generate quadrature signals compatible with those from anoptical rotary motion encoder in response to the motion of the fingeralong the axis.

Yet another embodiment disclosed includes a one-axis touch sensorconfigured for sensing an object along a single axis. The one-axis touchsensor is configured to generate a scrolling signal responsive tosensing motion of the object touching the one-axis touch sensor.

Still another embodiment disclosed includes a one-axis touch sensorcomprising a sensor configured to sense along a single axis. The sensoris configured to generate a quadrature signal responsive to an objecttouching the sensor. The quadrature signal including characteristics ofsignals being of the type produced by a rotary encoder.

Still another embodiment disclosed includes a one-axis touch sensorcomprising a sensor configured to sense a finger along a single axis ofthe one-axis touch sensor. A processor is in operative communicationwith the sensor. The sensor is configured to transmit to the processorone of a touch signal responsive to motion of the finger touching thesensor, and a lift signal responsive to lift off of the finger from thesensor. The processor is configured to generate a scrolling signalresponsive to the touch signal and the lift signal.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1A is a side plan view of a mouse typical of the prior art;

FIG. 1B is a top plan view of a mouse typical of the prior art;

FIG. 2A is a schematic view of a typical prior art rotary encoder;

FIG. 2B is a partial side plan view of a rotary disk and light detectoremployed by mice of the prior art;

FIG. 2C is a digital quadrature waveform generated by the rotary disk ofFIG. 2B;

FIG. 2D shows an alternative waveform to that of FIG. 2C;

FIG. 3A is a schematic view of a rotary encoder that operates oncapacitive principles rather than that which operates on opticalprinciples as depicted in FIG. 2A;

FIG. 3B is a partial side plan view of a notched disk and relatedcapacitance detector;

FIG. 3C is a depiction of a waveform as generated by the notched diskand capacitance detector of FIG. 3B;

FIGS. 3D and 3E are depictions of waveforms as generated by the notcheddisk and capacitance detector of FIG. 3B where the capacitance platesrotate in an opposite direction to that of FIG. 3C;

FIG. 4 is a partial schematic side view of a capacitive rotary encoderfor use herein;

FIG. 5 is a partial side plan view of a rotary encoder as an enhancementof the encoder depicted in FIG. 3A;

FIG. 6 is a partial schematic side view of a mechanism for capacitivelysensing mouse motion;

FIG. 7 is a partial schematic side view of a capacitance detector andcapacitance measurement circuit for use herein;

FIGS. 8A and 8B are side views of typical capacitive switches housedwithin a mouse enclosure;

FIG. 9 is a partial schematic side view of a scrolling wheel, capacitiverotary encoder and processor for use herein;

FIG. 10 is a partial schematic view of a further version of a capacitivescrolling control for use in the present invention;

FIGS. 11A through 11D are side and top plan views, respectively, of amouse enclosure showing plates for capacitive sensing;

FIGS. 12A through 12E are side views of sensors mounted for use herein;

FIGS. 13A through 13D are schematic views of alternative patterns forsensors for use herein;

FIG. 14 is a top plan view of a mouse enclosure and scrolling area foruse in creating the present capacitive mouse;

FIG. 15 is a graphical depiction showing total summed capacitance signalover time in employing the capacitive mouse of the present invention;

FIGS. 16A through 16C are graphical depictions of the coasting featureof the present invention;

FIG. 17 is a side view of a mouse enclosure housing the capacitivefeatures of the present invention; and

FIG. 18 is a schematic view of a scrolling module for use as a componentof the present capacitive mouse.

DETAILED DESCRIPTION

The following description of preferred embodiments of the disclosure isnot intended to limit the scope of the invention to these preferredembodiments, but rather to enable any person skilled in the art to makeand use the invention.

For reference, FIG. 1A shows the elements of a conventional prior artmouse 100 in side view. Enclosure 102, typically of hard plastic, formsthe body of the mouse. Ball 104 protrudes from the bottom of enclosure102 through a small hole. Motion of the mouse over a flat surface causesball 104 to rotate; this rotation is measured by rotary encoders 106.Typically two rotary encoders are used to measure motion of the mouse intwo orthogonal axes. Buttons 108 form part of the top surface ofenclosure 102. Finger pressure on buttons 108 is detected by switches110 mounted below the buttons. Scroll wheel 112 is mounted betweenbuttons 108; its rotation is measured by rotary encoder 114. Inputs fromrotary encoders 106 and 114 and switches 110 are combined by processor116 and transmitted to a host computer via cable 118.

FIG. 1B shows the same mouse 100 in top view, featuring enclosure 102,ball 104, buttons 108, scroll wheel 112, and cable 118.

FIG. 2A shows a typical prior art rotary encoder 200. Rotation of ball202 causes shaft 204 to spin, thus rotating notched disc 206. Lightemitter 208 passes light beam 214 through the notches of disc 206 tolight detector 210. As disc 214 spins, the pattern of signals fromdetector 210 allows processor 212 to deduce the direction and speed ofrotation. Note that shaft 204 is excited only by rotation of ball 202about an axis parallel to shaft 204. By mounting a second rotary decoder(not shown) perpendicular to rotary decoder 200, rotation of ball 202about two axes, and hence motion of the mouse in a two-dimensionalplane, can be detected.

FIG. 2B shows a detail view of notched disc 206 and light detector 210.Detector 210 actually contains two light sensitive elements 220 and 222spaced closely together relative to the spacing of notches 224. As disc206 rotates in the direction indicated by arrow 226, light sensitiveelements 220 and 222 are first both exposed to light through notch 224,then element 220 is eclipsed by the body of disc 206, then element 222is also eclipsed, then element 220 is exposed to light through adjacentnotch 228, then element 222 is also exposed to light through notch 228.Sensors 220 and 222 thus generate the digital quadrature waveform shownin FIG. 2C over time. If disc 206 rotates in the direction oppositearrow 226, the sensors are eclipsed in the opposite order and theygenerate the digital waveform shown in FIG. 2D. By digitally reading theoutputs of light sensors 220 and 222 and decoding the quadrature signalstherein, the processor can determine the direction and amount of motionof disc 206.

In an alternate embodiment, light sensitive elements 220 and 222 can beseparated and placed at analogous positions within two distinct notchpositions of disc 206. This embodiment is preferable if the lightsensors 220 and 222 are too large to be placed closely together; thedisadvantage is that it is more difficult to align sensors 220 and 222precisely relative to one another.

FIG. 3A shows a rotary encoder 300 that operates on capacitive insteadof optical principles. Ball 302 spins shaft 304 and notched disc 306.Shaft 304 and disc 306 are made of a conductive material such as metal,and the assembly consisting of shaft 304 and disc 306 is electricallygrounded by grounding element 308. Capacitance detector 310 measures thecapacitive effects of grounded disc 306. Various methods for grounding aspinning object, such as metal brushings, are known in the art.Alternatively, only disc 306 can be made conductive, with ground 308applied directly to disc 306. In yet another alternative embodiment,disc 306 is capacitively coupled to a nearby grounded object. In yetanother embodiment, a transcapacitance measurement may be done betweenthe body of disc 306 and detector 310, possibly by driving atime-varying signal into disc 306 and measuring the amplitude ofcoupling of that signal onto detector 310. In any case, capacitancedetector 310 measures the position of disc 306 by its capacitiveeffects, and the resulting signals are read by processor 312.

FIG. 3B shows a detail view of notched disc 306 and capacitance detector310. As in the case of the optical detector of FIG. 2B, capacitancedetector 310 is formed of two conductive plates 320 and 322 placed nearbut not touching the plane of disc 306. When notch 324 of disc 306 issituated adjacent to plates 320 and 322, those plates each have a lowcapacitance to ground. As the body of disc 306 moves to be adjacent toplate 320 and then to plate 322, the capacitance to ground of theseplates rises to a higher level. Because capacitance is linearly relatedto the area of overlap of conductive plates, this rise of capacitance ofplate 320 is linear. As disc 306 completely covers plate 320 and beginsto cover plate 322, the capacitance of plate 320 stays relativelyconstant while the capacitance of plate 322 linearly rises. As disc 306continues to rotate in the direction of arrow 326, the capacitance ofplate 320 and then plate 322 falls linearly, as depicted in thewaveforms of FIG. 3C. If disc 306 rotates in a direction opposite arrow326, the capacitances of plates 320 and 322 instead generate thewaveform of FIG. 3D.

Those experienced in the art will recognize that plates 320 and 322 maybe actual metal plates, or they may equivalently be conductive regionsformed in a variety of ways, including but not limited to conductive inkpainted or screened on a surface or substrate, conductive material suchas metal or indium tin oxide plated or otherwise disposed on a surfaceor substrate, or any other conductive object with at least onesubstantially flat portion placed in close proximity to disc 306.Similarly, the conductive notched disc 306 may be an actual notchedmetal disc, or it may be a notched conductive pattern formed on adisc-shaped substrate. The dielectric component of the capacitancebetween plates 320 and 322 and disc 306 may be an empty gap, a coating,surface, substrate, or other intermediary object, or some combinationthereof whose thickness and dielectric constant yield a convenientlymeasurable capacitance.

Those experienced in the art will further recognize that rotarycapacitive sensors are not limited to the disc configuration. Anyarrangement in which an irregular conductive object rotates near aconductive sensor will work equally well. In one alternate embodiment,disc 306 is extruded to form a rotating drum with a notched or patternedconductive surface, and plates 320 and 322 are oriented along the longdimension of the drum. The drum embodiment is bulky and mechanicallymore complex, but allows a larger area of capacitive overlap and hence astronger capacitance signal. In another alternate embodiment, thenotched disc could be simplified to a single “notch,” resulting in asemicircular conductive cam facing quarter-circle plates 320 and 322.

One way to process the capacitance signals from plates 320 and 322 is tocompare them against fixed capacitance thresholds. Referring to FIGS. 3Dand 3E, comparing capacitance 340 against threshold 344 yields digitalwaveform 348; similarly, comparing capacitance 342 against threshold 346yields digital waveform 350. Note that waveforms 348 and 350 of FIG. 3Eare identical in nature to the digital waveforms of FIG. 2D. Hence, ifthreshold comparison is used in this manner to generate digitalwaveforms, these digital waveforms can be processed by a processor 312identical to processor 212 of the conventional optical rotary encoder ofFIG. 2B.

Capacitance detector 310 can use any of a number of methods formeasuring capacitance as are known in the art. U.S. Pat. No. 5,880,411discloses one such capacitance measuring circuit.

As in the case of the optical encoder of FIG. 2A, note that plates 320and 322 may be placed adjacent to different notches as long as theirpositioning within their respective notches is maintained. However,since plates 320 and 322 do not require housings or packages outside theplates themselves, it is convenient to place them side by side mountedon a common substrate in order to ensure that they will remain alignedto each other.

One skilled in the art will observe that by examining the originalanalog capacitance waveforms of FIGS. 3C and 3D, it is possible tolocate disc 306 to a much finer resolution than the notch spacing. Thisis because at any given point in time, one of the capacitance signals isvarying linearly with disc rotation while the other is constant. Bytracking these linear variations, processor 312 can track disc rotationat a resolution limited only by the resolution and linearity of thecapacitance measurements. In the preferred embodiment, the circuitsdisclosed in U.S. Pat. No. 5,880,411 are used to perform these precisecapacitance measurements.

Because disc rotation can be measured to much higher resolution than thenotch spacing, it is possible to use much larger notches on disc 306,and correspondingly larger plates 320 and 322, than are feasible for theanalogous notches and sensors of the optical encoder of FIG. 2A. Largernotches and plates allow mechanical tolerances of the assembly to berelaxed, yielding potentially lower costs. Even with larger notches andplates, a capacitive rotary encoder can produce higher-resolution datathan an optical rotary encoder if a sufficiently high-resolutioncapacitance detector is used. Larger plates 320 and 322 also result in alarger capacitance signal which is easier for detector 310 to measure.

The plates 320 and 322 and grounding mechanism 308, being simple formedmetal pieces or plated conductive patterns, may also be less costly thanthe semiconductor light emitters and sensors of FIG. 2A.

Another advantage of the capacitive rotary encoder is that it is notaffected by optically opaque foreign matter, such as dirt, which may bepicked up and introduced into the assembly by ball 306. The loosermechanical tolerances allowed by the capacitive rotary encoder may alsomake it more resistant to jamming by foreign matter.

FIG. 4 shows a side view of the capacitive rotary encoder, with disc 400and plates 402 and 404 separate by a gap 406. Gap 406 is drawn large forillustrative purposes, but in the preferred embodiment gap 406 is keptas small as possible to maximize the capacitance between disc 400 andplates 402 and 404. If gap 406 is small, and the tolerances of theencoder assembly are loose as previously disclosed, then movement ofdisc 400 along the axis of shaft 408 will have a proportionately largeeffect on the width of gap 406. This variation can impact the accuracyof the capacitance measurements of plates 402 and 404. FIG. 5 shows anenhancement to the arrangement of FIG. 3A that solves this problem.

In FIG. 5, disc 500 is adjacent to three plates 502, 504, and 506.Plates 502 and 504 are identical to plates 320 and 322 of FIG. 3A. Plate506 is the size of plates 502 and 504 combined, and is located nearplates 502 and 504; in FIG. 5, plate 506 occupies the next notch spaceafter plates 502 and 504. In an alternative embodiment, matching couldbe improved by splitting plate 506 into two half-plates each exactly thesize of plates 502 and 504. In the system of FIG. 5, the processorcomputes the sum of the capacitance measurements from plates 502, 504,and 506. Note that the total overlap area between disc 500 and plates502, 504, and 506 is constant regardless of the rotary position of disc500. Hence, the summed capacitance of plates 502, 504, and 506 should beconstant. Variation in this sum indicates that disc 500 has shiftedrelative to plates 502, 504, and 506, for example, by moving along theaxis as shown in FIG. 4. The processor divides each plate capacitancemeasurement by the summed capacitance in order to normalize thecapacitance measurements. These normalized measurements are invariant ofthe width of gap 406 of FIG. 4, and are suitable for use in the positioncomputations previously discussed.

FIG. 6 shows an alternative mechanism for capacitively sensing mousemotion. This mechanism employs a rolling ball 602 protruding from a holein enclosure 600 similar to that of a conventional mouse. The surface ofball 602 is patterned with regions 604 of higher and lower conductivity.This patterning can be accomplished by forming the ball of material suchas rubber of varying conductivity, or by treating the surface of theball with conductive substances such as paint or metal. The conductivesurface of the ball may be protected if necessary by a dielectric outerlayer 606. Capacitance detectors 608 are placed in several locationsproximate to ball 602. As the ball rolls, the conductive regions 604will move from one capacitance detector to another; processor 610correlates these signals to measure the movement of ball 602. Becausethe capacitance measurements vary linearly as conductive region 604moves from one detector 608 to another, processor 610 can interpolate inorder to measure movement of the ball to very high resolution.

The system of FIG. 6 requires several sensors 608 in order to ensurethat at least one conductive region 604 is detectable at all times.Conductive regions 604 should be as large as possible in order tomaximize the capacitive signal, subject to the constraint that differentregions 604 should be separated by enough distance to allow individualregions 604 and the spaces between them to be resolved by detectors 608.Hence, the spaces between regions 604 should be at least comparable tothe size of detectors 608, and the conductive regions 604 should be atleast a significant fraction of the size of detectors 608.

FIG. 6 depicts a linear row of sensors 608 curved around the surface ofball 602. Such an arrangement can detect rolling of the ball in onedimension; the example of FIG. 6 would detect the rolling resulting frommotion of the mouse along axis 612. In the preferred embodiment, othersensors (not shown) are arranged in a row perpendicular to the row ofsensors 608 in order to measure motion of the mouse in two dimensions.

In one embodiment, the conductive regions in the ball are grounded tofacilitate capacitance measurements by simple conductive plates.However, grounding the conductive regions of the ball may beimpractical, so in the preferred embodiment, capacitance detectors 608measure transcapacitance.

FIG. 7 shows one simple way to measure transcapacitance. The capacitancedetector 700 consists of two plates 702 and 704. Plate 702 is connectedto ground, and plate 704 is connected to a capacitance measurementcircuit 706. Proximity to an electrically floating conductor 708 withinball 710 creates a capacitive coupling 712 from plate 702 to conductor708, and a capacitive coupling 714 from conductor 708 to plate 704,hence effectively coupling plate 702 to plate 704 through two seriescapacitances. Those experienced in the art will recognize that manyother configurations of plates 702 and 704 are possible, such asinterdigitated lines or concentric circles and toroidal shapes. In stillanother embodiment of capacitance detector 700, plate 702 could bedriven with a time-varying signal which is capacitively coupled ontoplate 704 and detected by circuit 706.

The motion sensor of FIG. 6 requires even fewer moving parts than thatof FIG. 3, and thus can lead to an even cheaper and more physicallyrobust mouse. However, the system of FIG. 6 has the disadvantage ofrequiring more complex processing in processor 610.

Other methods for detecting mouse motion are known in the art, such asthe optical methods of U.S. Pat. Nos. 4,546,347 (Kirsch) and 5,907,152(Dandiker et al.). Fully solid-state optical motion detectors would pairwell with the capacitive button and scrolling controls of the presentinvention to form an entirely solid-state optical/capacitive mouse.

Mice conventionally include one or more buttons as well as a motiondetector. Referring back to FIG. 1, button 108 is typically linked to amechanical switch 110. By pressing down on the surface of switch 108,the user closes switch 110. Mechanical switches have various well knowndisadvantages. Since they have moving parts, mechanical switches canfail over time or with rough handling. Also, mechanical switches requirea certain threshold of pressure for activation, which can tire the userwith repeated use.

Mechanical switches can be replaced by capacitive sensors in severalways. FIG. 8A shows one type of capacitive switch that is well-known inthe art. Mouse enclosure 800 is shaped similarly to that of aconventional mouse, but with no moving parts in its top surface.Conductive plate 802 is placed on or near the surface of the enclosure,preferably covered by a protective dielectric layer 806. Capacitancemeasurement circuit 804 monitors the capacitance of plate 802. When afinger (not shown) touches surface region 806, the capacitance to groundof plate 802 increases beyond a threshold set by measurement circuit804. When no finger is present, the capacitance to ground of plate 802is below the threshold. By comparing the capacitance of plate 802 to thethreshold, circuit 804 can generate a digital signal which is equivalentto the signal produced by a mechanical switch.

The system of FIG. 8A implements a mouse button which requires zeroactivation force; indeed, depending on the threshold setting, it couldeven be sensitive to mere proximity of the finger. Although this mousebutton solves the problem of tiring the finger during repeatedactivations, it introduces the converse problem of tiring the fingerduring periods of inactivity, since the finger must not be restedagainst surface 806 without accidentally activating the button.

FIG. 8B shows a second type of capacitive switch, also well-known in theart. Enclosure 820 includes a separate movable button portion 822 as ina conventional mouse. Instead of a mechanical switch beneath button 822,there is a conductive plate 826 and some sort of spring mechanism 824. Avariety of mechanisms 824 are usable and well-known, including but notlimited to metal springs, compressible foam, or single-piece enclosureswith buttons made of springy material. Spring mechanism 824 mayoptionally also include a tactile feedback means to impart the familiarclicking feel to button activations. A second conductive plate 828 ismounted beneath plate 826 so that pressure on button 822 brings plate826 measurably closer to plate 828, thus increasing the capacitancebetween plates 826 and 828. Capacitance measuring circuit 830 detectsthis change in capacitance to form a button signal.

Because the system of FIG. 8B works by measuring the capacitance betweenplates 826 and 828, these plates do not need to make electrical contactin order to activate the button. Indeed, these plates must be kept outof electrical contact in order for capacitance measuring circuit 830 tooperate properly. Many straightforward ways are known to separate plates826 and 828, including but not limited to an insulating surface on plate826, plate 828, or both plates, or an insulating compressible foamplaced between the plates.

The system of FIG. 8B is very similar to a conventional mechanicalswitch, but it is more resistant to dirt and wear because buttonactivation does not require an electrical contact to be made.

Capacitance measuring circuits 804 and 830 may use any of a variety ofwell-known capacitance measuring techniques. In the preferredembodiment, a circuit like that disclosed in U.S. Pat. No. 5,880,411 isused.

Many mice also include a scrolling mechanism. This mechanism typicallyemploys a rotating wheel, an isometric joystick, or a set ofdirectionally arranged buttons; the scrolling mechanism 112 is typicallymounted between two mouse buttons 108 as shown in FIG. 1B.

FIG. 9 shows one way to measure a scrolling command capacitively. Ascrolling wheel 902 is mounted in mouse enclosure 900, seen in sideview. The wheel appears to the user to be the same as the wheel of theconventional mouse of FIGS. 1A and 1B. Rotation of the wheel is measuredby capacitive rotary encoder 904 and processor 906 similar to those ofFIGS. 3A and 3B. The capacitive rotary encoder 904 can be mounteddirectly on the axis of scrolling wheel 902 as shown in FIG. 9, or wheel902 can be mechanically linked to a separate rotary encoder mechanismelsewhere in enclosure 900.

FIG. 10 shows another capacitive scrolling control. A scrolling knob1002 protrudes from mouse enclosure 1000. Knob 1002 is connected bystick 1004 to conductive plate 1006 and to spring mechanism 1008.Depending on the stiffness of spring 1008, knob 1002 may act as either arocking control or an isometric joystick. Conductive plates 1010 and1012 are mounted near plate 1006, and capacitance measuring circuit 1014measures the capacitances between plate 1010 and plate 1006, and betweenplate 1012 and plate 1006. When knob 1002 is pressed in a forward orbackward direction, plate 1006 is deflected slightly to produce ameasurable change in the capacitances of plates 1010 and 1012. Bycomparing the capacitances of plates 1010 and 1012, circuit 1014 candetect this forward or backward deflection to produce a scrollingcommand. Also, by noting an increase in capacitance of both plates 1010and 1012 at once, circuit 1014 can detect downward pressure exerted onknob 1002. Many conventional mice use a downward deflection of thescrolling control as an additional command signal, such as theactivation of a third mouse button.

By placing two additional plates along an axis perpendicular to the axisof plates 1010 and 1012, it is possible to measure deflection of knob1012 in three dimensions. Sideways deflection of knob 1012 can beinterpreted as a command for horizontal scrolling, or panning. Forwardand backward deflection can be interpreted as vertical scrolling, anddownward deflection can be interpreted as an additional mouse button orother special command.

In an alternate embodiment, plates 1010 and 1012 are situated aboveplate 1006 so that pressure on knob 1002 causes plate 1006 to deflectaway from plates 1010 and 1012, and the measured capacitance on plates1010 and 1012 to decrease with pressure instead of increasing. Thoseskilled in the art will recognize that the processing necessary for thisembodiment is identical to that required for the embodiment of FIG. 10except for a change of sign.

The systems of FIGS. 9 and 10 share the disadvantage that they are stillmechanical devices with moving parts. For greatest robustness andsensitivity and lowest cost, a truly solid state solution to scrollingis preferable.

FIG. 11A shows a scrolling control that operates directly on capacitivesensing principles. Mouse enclosure 1100 contains an array of conductiveplates 1102 connected to a processor 1104 that includes capacitancemeasuring circuits. Plates 1102 are insulated from the user's finger bysurface 1106. In the preferred embodiment, the array of plates 1102 isplaced in between two mouse buttons 1108 as shown in FIG. 11B. Manyalternate embodiments in which the scrolling control is placed elsewhereare possible, such as the embodiment of FIG. 11C in which the scrollingcontrol is mounted on the side of mouse enclosure 1100 for access by theuser's thumb. The mouse buttons 1108 of FIGS. 11B and 11C could becapacitive buttons as previously disclosed, or conventional mechanicalswitches or any other suitable type of button.

FIG. 11D shows yet another configuration, in which scrolling sensors1102 are placed on top of a conventional mouse button 1108; pressingdown on button 1108 without substantially moving the finger produces abutton click, while lightly touching button 1108 and then moving thefinger generates scrolling.

Preferably, plates 1102 are numerous and spaced closely together so asto allow interpolation of the finger position to greater resolution thanthe plate spacing. In one preferred embodiment, nine plates are usedspanning a distance of approximately one inch. U.S. Pat. No. 5,880,411discloses a preferred method for measuring the capacitances of an arrayof sensors and interpolating the finger position from those measuredcapacitances. Many other methods are possible and well-known in the art,such as that of U.S. Pat. No. 5,305,017 to Gerpheide.

Once the finger position among plates 1102 is known, motion of thefinger along the axis of plates 1002 can be measured by comparing fingerpositions at successive times. Processor 1104 generates a scrollingsignal of a certain direction and distance when a finger motion of acorresponding direction and distance is measured. The effect as observedby the user is as if the user were rolling a wheel like wheel 902 ofFIG. 9 by moving the finger forward and backward on the top edge of thewheel. Instead, the user moves the finger forward and backward alongsensor surface 1106 to produce the identical scrolling signals.

In any scrolling mouse, but particularly in a capacitive scrollingmouse, it may be desirable to provide for different regimes of low-speedand high-speed scrolling in order to account for the fact that thescroll surface 1106 is much shorter than a typical scroll bar in atypical graphical user interface. A simple way to provide for differentspeed regimes is to use the technique commonly known as “acceleration”or “ballistics” when applied to mouse motion signals. In this technique,very small finger motions translate to disproportionately small scrollsignals, and very large finger motions translate to disproportionatelylarge scroll signals.

In the preferred embodiment, processor 1104 measures the total amount offinger signal as well as the finger position, and generates a scrollingsignal only when sufficient finger signal is present. Otherwise, thescrolling signal when no finger was present would be ill-defined, andthe mouse would be prone to undesirable accidental scrolling. In thepreferred embodiment, processor 1104 compares the total summedcapacitance on all sensors 1102 against a threshold to determine fingerpresence or absence; in an alternate embodiment, processor 1104 insteadcompares the largest capacitance signal among all sensors 1102 against athreshold. The threshold should be set high enough so that onlydeliberate finger actions result in scrolling. If the threshold is settoo low, the mouse may scroll in response to mere proximity of thefinger, in general an undesirable feature.

There are many ways to mount sensors 1102 under surface 1106. Some ofthese ways are depicted in FIGS. 12A through 12E. Those experienced inthe art will realize that many other mounting schemes are possible, andthat the particular choice of mounting scheme does not alter the essenceor the basic operation of the invention.

In FIG. 12A, scrolling surface 1202 is an uninterrupted region ofenclosure 1200. Sensors 1204 are affixed to the back surface ofenclosure 1200 using adhesive or other intermediary substance 1206.Adhesive 1206 could be eliminated by the use of a self-adhesive sensormaterial 1204 such as conductive paint. Wires or other conductorsconnect sensors 1204 to processor 1208.

In FIG. 12B, sensors 1204 are disposed on a substrate material 1206which is then affixed to the back surface of enclosure 1200. Sensors1204 might be composed of conductive ink, indium tin oxide, metal foil,or any other conductive material. Substrate 1206 might be polyesterfilm, plastic, glass, or any other material on which conductive sensorscan be disposed. In the example of FIG. 12B, substrate 1206 bends awayfrom enclosure 1200 to carry the conductive signals from sensors 1204 toprocessor 1208.

In FIG. 12C, the material of enclosure 1200 in or near scrolling region1202 has been made thinner than normal in order to increase thecapacitive coupling from sensors 1204 to the finger. Additionally,sensors 1204 have been disposed on the opposite side of substrate 1206in order to increase their proximity to the finger. To strengthen theenclosure, solid backing 1210 can optionally be placed behind thesensors. Layer 1210 may also be made conductive and electricallygrounded in order to isolate sensors 1204 from interference from othercircuits within the mouse. A similar grounded shield may be used in anyof the other sensor arrangements disclosed herein.

In FIG. 12D, substrate material 1206 leads out through hole 1212 to thesurface of enclosure 1200. In this example, substrate 1206 itself formsthe protective dielectric layer 1202 between sensors 1204 and thefinger. Hole 1212 may be protected and disguised in various ways, suchas by combining hole 1212 with the opening around the edge of amechanical mouse button.

In FIG. 12E, sensors 1204 are embedded directly into the material ofenclosure 1200, for example in the form of wires or foil strips encasedin plastic.

When sensors 1204 are disposed on a substrate 1206, it is convenient touse an extension of substrate 1206 to carry the sensor signals toprocessor 1208, as shown in FIGS. 12B, 12C, and 12D. In these cases,sensors 1204 and their associated wiring may be patterned on substrate1206 using conductive ink or other suitable material. FIGS. 13A to 13Dshow several of the many possible patterns.

In FIG. 13A, substrate 1300 extends beyond the area of sensors 1302 onone side. This side extension 1306 forms a carrier for the sensorsignals 1304 to a processor 1308. Processor 1308 may be mounted to theside of sensor area 1302 as shown, or it may be mounted beneath sensor1302 or in another location, with extension 1306 bending, folding, orwarping as it leads away from sensor 1302.

In FIG. 13B, signals 1304 bend at 90 degrees and extension 1306 leadsaway along the length of the area of sensors 1302.

FIG. 13C is similar to FIG. 13B, but sensors 1304 leave the area ofsensors 1302 on both sides in order to balance the extension ofsubstrate 1300 to the sides of the area of sensors 1302.

In FIG. 13D, two layers of conductive material are used with aninsulating layer or substrate between. The conductive first layercontains sensors 1302. The second conductive layer contains sensorsignals 1304 running in a direction perpendicular to sensors 1302. Vias1310 penetrate the insulating layer to connect sensors 1302 to signalwires 1304. In crossings 1312 of wires 1304 over sensors 1302 withoutvias, the two conductive layers are electrically isolated although therewill be some capacitive coupling that processor 1308 must take intoaccount. The sensor of FIG. 13D will be more expensive due to its use ofadditional layers, but it avoids any extension of substrate 1300 aroundthe area of sensors 1302. Such extension may be undesirable for designor aesthetic reasons, in addition to providing opportunities forundesirable capacitive coupling between the finger and wires 1304 whenthe finger touches near but not directly in the area of sensors 1302.The latter undesirable capacitive coupling can also be remedied by theaddition of a grounded shield over the exposed wires 1304, as shown byregion 1314 of FIG. 13B.

Yet another embodiment of the capacitive scrolling control is shown inFIG. 14. Mouse enclosure 1400 includes a two-dimensional scrolling area1402 preferably disposed between mouse buttons 1408. Scrolling area 1402includes an array of sensors 1404 disposed in one direction, and asecond overlapping array of sensors 1406 disposed in a substantiallyperpendicular direction to form a two-dimensional matrix. Each array ofsensors is processed using methods analogous to FIGS. 11 through 13; theposition results from the two arrays are combined to form the completefinger location in two dimensions.

Two-dimensional capacitive touch sensors, or touch pads, are well knownin the art. In the preferred embodiment, the methods of U.S. Pat. No.5,880,411 are used. FIG. 2 of the '411 patent illustrates a diamondpattern for sensor matrix 1402 which is preferred due to variousadvantages disclosed in that patent. Many other sensing techniques andsensor geometries are known in the art.

Once the finger position in two dimensions is known, finger motion inthe horizontal and vertical directions can be measured by comparingfinger positions at successive times. Horizontal finger motiontranslates to horizontal scrolling, or panning. Vertical finger motiontranslates to vertical scrolling. In one embodiment, diagonal fingermotion translates to simultaneous horizontal and vertical scrolling. Inan alternate embodiment, the horizontal and vertical motion signals arecompared to discover whether the finger motion is primarily horizontalor primarily vertical, and the corresponding type of scrolling isapplied.

Scrolling wheel mice like that of U.S. Pat. No. 5,530,455 typicallycontain an additional switch to sense when the wheel is pressed down bythe user. This switch generates a signal similar to a third mouse buttonsignal for enabling additional scrolling or other features in hostsoftware. A comparable switch could be mounted beneath the capacitivetouch sensors of FIGS. 11 through 14, but other methods are preferred inorder to avoid the cost and reliability problems inherent in switches.

One way to simulate a third mouse button in a capacitive scrollingcontrol is to decode tapping gestures using the various methodsdisclosed in U.S. Pat. No. 5,880,411. In the most simple case, basicfinger taps are decoded and translated into simulated clicks of thethird mouse button. FIG. 15 shows the total summed capacitance signalover time, and the corresponding third button signal resulting from tapdetection. The '411 patent discloses many additional refinements for tapdetection on capacitive touch sensors, many of which are suitable forapplication to scrolling controls.

A second way to simulate a third mouse button is to introduce anadditional touch sensor plate which forms a capacitive button asdisclosed in FIG. 8A or 8B.

Arrayed capacitive touch sensors, particularly two-dimensional sensorslike that of FIG. 14, can resolve numerous additional types of inputthat more specialized sensors like wheels and isometric joystickscannot. One example is the use of multiple fingers to activate specialmodes or user interface commands; U.S. Pat. No. 5,880,441 discloses oneembodiment of multi-finger sensing. Another example is graphic gestures,where looping motions and other finger motions that are not entirelyhorizontal or vertical can be interpreted as special user interfacecommands. Yet another example is special designated zones in whichfinger motion or tapping invokes special behaviors.

Because the capacitive scrolling control feels similar to a scrollingwheel to the user, other techniques may be employed to strengthen thewheel analogy. One such technique is “momentum” or “coasting,” in whichscrolling behavior is adjusted based on the velocity of finger motion asthe finger lifts away from the scroll sensor.

FIGS. 16A and 16B illustrate the basic coasting feature. Each figureshows the finger presence or absence, the computed finger motion, andthe resulting scrolling signal generated by the mouse. For simplicity,motion and scrolling in only one dimension are considered as in the caseof FIG. 11; the two-dimensional scrolling of FIG. 14 leads to astraightforward generalization of FIG. 16. Note that the finger motionis undefined when the finger is absent; in FIGS. 16A and 16B, the motionis plotted as zero when the finger is absent for purposes ofillustration.

In FIG. 16A, the finger touches the scrolling sensor, moves back andforth to generate a corresponding back-and-forth scrolling signal, thencomes to a complete stop before lifting. When the processor observes azero or near-zero velocity as the finger lifts, it ceases all scrollingactivity; coasting does not occur.

In FIG. 16B, the finger executes the same scrolling motions, but thenmoves again and lifts while still moving. When the processor observesthat the velocity was substantially non-zero as the finger beganlifting, the processor continues scrolling in a direction and speeddetermined by the final velocity of the finger upon lifting. The effectas seen by the user is that the imaginary scroll wheel is left spinning,or coasting, by the finger motion on it. In the preferred embodiment,the coasting speed and direction are equal to the scrolling speed anddirection just before the finger lifted, though in alternateembodiments, the coasting speed could be constant or the coasting speedand direction could be some other function of the final scrolling speedand direction.

To terminate coasting, the user simply returns the finger to thescrolling control as seen in FIG. 16B. No special processing is neededto accomplish this aspect of coasting: As soon as the finger returns tothe scrolling control, the coasting signal is replaced by fresh motionsignals, which are zero until the finger actually moves on the control.The effect as seen by the user is that the imaginary spinning scrollwheel is halted as soon as the finger is pressed on it. Coasting is avaluable aid to long-distance scrolling through large documents.

FIG. 16C shows an additional optional aspect of coasting, whereinfriction is simulated by having the coasting speed slowly decay to zeroas the finger is held off the scroll sensor. FIG. 16C shows an alternatescrolling signal to that of FIG. 16B in which friction slows thecoasting effect over time.

The user can still halt the coasting before it has come to a naturalstop by touching the finger back to the scrolling control.

Some mice offer other features in addition to motion, two buttons, andscrolling. Many of these features are also well suited to a capacitiveimplementation. One example is additional buttons for special functionssuch as Internet browsing. Another example is additional scroll-likefunctions such as a separate “zoom” control. Still another example is ageneral hand proximity sensor on the mouse enclosure that allows themouse and associated software to tell whether or not the user's hand isgripping the mouse. Those experienced in the art will recognize that thevarious types of capacitive sensors, buttons, rotary, linear andtwo-dimensional, are appropriate for a wide variety of applicationsbeyond those specific examples disclosed here.

Referring back to FIG. 1, any combination of one or more of the motionsensors 106, button sensors 110, scrolling sensors 114, and anyadditional sensors can be implemented by capacitive methods as disclosedherein. In typical mice, the signals from all these types of sensors,whether capacitive, mechanical, optical or otherwise are combined inprocessor 116 to produce a mouse signal to be sent to the host computer.Standard protocols are well known in the art for sending motion, button,and scrolling signals from a mouse to a host computer. These sameprotocols may be used when one, several, or all of the sensors areimplemented by capacitive techniques. Thus, the capacitive mouse of thepresent invention is fully interchangeable with conventional mice withno change to host mouse drivers or other system-level facilities.

It is possible and may be desirable to construct a mouse that uses acombination of capacitive, mechanical and other sensing techniques. Forexample, a capacitive scrolling sensor could be added to an otherwiseconventional mechanical mouse. Or, a capacitive motion sensor could beused on a mouse with mechanical buttons and no scrolling control at all.

If several or all sensor functions of the mouse are implementedcapacitively, it may be possible to use a single capacitive sensing chipfor all capacitive sensing functions. Thus, for example, if capacitivesensing is used on the mouse for scrolling, then it may cost little moreto implement the motion sensor capacitively as well using additionalinput channels of the same capacitance measuring chip.

It is possible to purchase mouse processor chips that perform all of thetasks of processor 116 or a conventional mouse. These chips generallyaccept motion and scrolling inputs in quadrature form as shown in FIGS.2C and 2D, and the buttons are implemented as switches which alternatelydrive an input pin to a high or low voltage.

FIG. 17 shows how a capacitive mouse 1700 can be built using aconventional mouse processor chip 1702 in conjunction with a capacitancemeasuring chip 1704. Ball 1706 drives capacitive motion sensor 1708,whose sensing plates connect to chip 1704. Scrolling sensors 1710 alsoconnect to chip 1704, as do the button sensors (not shown). Chip 1704computes motion and scrolling signals using the techniques disclosedherein, and then generates quadrature signals as outputs with timing andcharacteristics matching those produced by a true rotary sensor such asthat of FIG. 2A. Chip 1702 then converts these artificial quadraturesignals into standard mouse protocols. If quadrature is not appropriate,chips 1704 and 1702 could equally well use any other intermediate formfor transmitting motion data. Chip 1704 also measures the signals fromthe capacitive mouse buttons, and drives its digital output pins high orlow based on the observed button capacitances. Chip 1702 reads thesedigital button signals as if they came from mechanical switches. Thearrangement of FIG. 17 is not as cost-effective as a design with asingle chip that does all the tasks, but it may greatly simplify thedesign of a new mouse using a new protocol or other features not yetsupported by standard capacitive sensing chips.

Yet another alternative is to perform only rudimentary sensor processingon the mouse, producing an intermediate form such as the quadratureoutput by chip 1704 of FIG. 17. These signals can then be sent to a hostcomputer for final processing, thus relieving some of the load from thelow-cost mouse hardware. Another variation of this scheme is to sendfinger position data instead of fully processed scrolling motion datafor a capacitive scroll sensor.

FIG. 18 shows a scrolling module designed to be used as a component in amouse design. Circuit board 1800 includes an array of sensors 1802 aswell as a capacitive sensing chip 1804. Connector 1806 sends outquadrature signals compatible with conventional rotary encoders.Similarly, a self-contained rotary encoder module could be constructedusing capacitive sensors. Using these modules, an industrial designercould construct the mouse of FIG. 17 using only standard components,without requiring any expertise in capacitive sensing.

As any person skilled in the art will recognize from the previousdescription and from the figures and claims, modifications and changescan be made to the preferred embodiments of the invention withoutdeparting from the scope of the invention defined in the followingclaims.

1. A device comprising: an enclosure, the enclosure including anexternal surface and a back surface opposite the external surface; aflexible substrate including a first portion affixed to the backsurface, a second portion spatially separate from the first portion, anda bendable portion between the first portion and the second portion; anarray of sensors on the first portion of the flexible substrate, thearray of sensors configured to sense objects proximate the externalsurface; and a processor mounted to the second portion of the flexiblesubstrate, the processor electrically coupled to the array of sensors,the processor configured to generate an output in response to objectmotion capacitively detected by the array of sensors.
 2. The device ofclaim 1 wherein the external surface comprises a touch surface.
 3. Thedevice of claim 1, wherein the enclosure includes a first region affixedto the first portion, and wherein the first region is relatively thinnercompared to another region of the enclosure adjacent to the firstregion.
 4. The device of claim 1, further comprising: an adhesivecoupling the first portion to the back surface.
 5. The device of claim1, wherein the flexible substrate is between the array of sensors andthe back surface.
 6. The device of claim 1, wherein the array of sensorsis between the flexible substrate and the back surface.
 7. The device ofclaim 1, wherein the array of sensors is formed of conductive ink. 8.The device of claim 1, wherein the array of sensors is formed of indiumtin oxide.
 9. The device of claim 1, wherein the flexible substratecomprises a plastic material.
 10. The device of claim 9, wherein theplastic material comprises polyester.
 11. The device of claim 1, furthercomprising: a backing affixed to the flexible substrate.
 12. The deviceof claim 1, wherein the array of sensors comprises a first plurality ofsensors arranged in a first axis.
 13. The device of claim 12, whereinthe array of sensors further comprises a second plurality of sensorsarranged in a second axis, wherein the array of sensors is configured tosense the object motion in two dimensions.
 14. The device of claim 1,wherein the output is selected from a set consisting of: cursor motion,zooming, one-dimensional scrolling, and two-dimensional scrolling. 15.The device of claim 1, wherein the processor is configured to generatethe output by: applying ballistics.
 16. A device comprising: anenclosure, the enclosure including an external surface and a backsurface opposite the external surface, wherein the external surfacecomprises a touch surface; a flexible substrate including a firstportion affixed to the back surface by adhesive, a second portionspatially separate from the first portion, and a bent portion betweenthe first portion and the second portion; an array of sensors on thefirst portion of the flexible substrate, the array of sensors configuredto sense objects proximate the touch surface in two dimensions; and aprocessor mounted to the second portion of the flexible substrate, theprocessor electrically coupled with the array of sensors, the processorconfigured to generate an output in response to object motioncapacitively detected by the array of sensors.
 17. The device of claim16, wherein the flexible substrate is between the array of sensors andthe back surface.
 18. The device of claim 16, wherein the flexiblesubstrate comprises polyester
 19. A method of providing an output usinga capacitive device comprising an enclosure, the enclosure including anexternal surface and a back surface opposite the external surface, aflexible substrate including a first portion affixed to the backsurface, a second portion spatially separate from the first portion, anda bent portion between the first portion and the second portion, anarray of sensors on the first portion of the flexible substrateconfigured to sense objects proximate the external surface, and aprocessor mounted to the second portion of the flexible substrate, themethod comprising: operating the array of sensors to obtain signals;determining motion of an object proximate to the external surface usingthe signals; causing scrolling in response the object moving along afirst axis; causing continued scrolling in response to the objectlifting from the external surface with a substantially non-zero speedalong the first axis; and not causing continued scrolling in responsethe object lifting from the external surface with a substantially zerospeed along the first axis.
 20. The method of claim 19, furthercomprising: decaying the continued scrolling.